By some measures, chemical plants like the sites of separate fatal explosions this week in Louisiana are among the safest manufacturing workplaces in America. That doesn’t stop residents and emergency responders from keeping wary eyes on the hundreds of facilities stretched along the Mississippi River from New Orleans to Baton Rouge.

Because of the volatile nature of many of the products they make, explosions, chemical releases and other accidents are real threats. Emergency officials say they’re well-drilled to respond but residents do worry about what can happen next door.

The threat was underscored Friday when a second fatal explosion occurred at a plant located just miles away from the site of the previous day’s deadly blast.

“For the most part, day to day, month to month, year to year, you don’t really think about it,” said Ascension Parish Councilman Travis Turner, who lives about 4 miles from the plant in Geismar where the earlier explosion occurred. “Everybody knows somebody — a brother or cousin or uncle — who works at a plant. When something happened, everybody is worried about the worst case scenario, like yesterday.”

State and local officials have welcomed oil refineries, chemical plants and related industries, with their heavy capital investments and good-paying jobs. Louisiana is experiencing a boom in new plants and expansions, driven by low natural gas prices, as well as the area’s strategic advantages.

Louisiana Economic Development counts more than $30 billion in investments announced in Louisiana starting in 2011, and that doesn’t include a number of upgrades. Among them is a $400 million expansion at the Williams Companies Inc. plant where two workers were killed and dozens more were injured as a result of a Thursday explosion that was heard for miles.

On Friday night, a separate, smaller explosion occurred miles away in Donaldsonville, killing one person and injuring seven others, the state police said. Workers were offloading nitrogen by hose from an 18-wheeler and pressurizing a metal “vessel” when it failed, causing the explosion at a CF Industries facility that makes ammonia and other nitrogen fertilizers, Sandifer said.

Donaldsonville and Geismar are both located in Ascension Parish and straddle the Mississippi River, between New Orleans and Baton Rouge.

The workers killed as a result of Thursday’s blast were Scott Thrower, 47, of St. Amant, and Zachary Green, 29, of Hammond. Thrower succumbed to his injuries Friday.

The U.S. Labor Department’s Occupational Safety and Health Administration was investigating. A department spokesman and company officials said the cause of the blast wasn’t immediately known, but the FBI ruled out terrorism.

It might be easy to conclude that working in a chemical plant is a dangerous occupation, but statistics say otherwise. There were 25 fatalities in chemical manufacturing plants nationwide in 2011, according to the Bureau of Labor Statistics. That’s a fatality rate of 1.9 per 100,000 full-time workers, barely half the rate among all workers.

Nationwide, 3.8 of every 100 full-time workers was injured in 2011, according to the U.S. Occupational Safety and Health Administration. The injury rate was 2.4 in the overall chemical manufacturing sector, and 0.6 in the area of chemical manufacturing including the Williams plant. That’s among the very lowest injury rate of any manufacturing sector.

Ron Perry, the emergency preparedness director in St. Charles Parish, said that concerns about chemical accidents rank “somewhere in the middle” of his list of worries. Hurricanes are at the top this time of year. Besides about 25 major oil and chemical facilities, there’s also a nuclear power plant. Large plants have internal firefighting forces, and fire departments and plants agree to help each other. Perry said such mutual-aid agreements actually make the large concentrations of industry safer.

Incidents large and small do occur in Louisiana, driven in part by the extraordinary density of the chemical and refining industries along the lower Mississippi River, sometimes likened to Germany’s industrial Ruhr region. Only the Houston area can compare to Louisiana’s corridor, where the Mississippi provides fresh water and transportation and where an intricate system of pipelines carries raw materials to plants and products away. According to a Louisiana Chemical Association report issued in March, there were 311 chemical manufacturers with 15,727 employees in parishes along the Mississippi River from Baton Rouge to its mouth in 2012. These numbers exclude oil refiners, themselves a major presence, and some plastics manufacturers.

“It’s a very important sector in our economy,” said Iain Vasey, executive director of business development for the Baton Rouge Area Chamber of Commerce. “Generally these are very desirable jobs because they are highly paid and highly skilled.”

The average salary at new and expanding plants announced since 2011 is nearly $70,000, according to the state. That’s significantly above the median household income of about $43,000 a year in Louisiana.

Geismar is one of the major nodes of the industry, tucked among former sugar cane fields along the river about 20 miles south of Baton Rouge. Last year, the Westlake Chemical Corp. in Geismar, which makes ingredients for plastics, suffered a fire in March following a runaway chemical reaction. Residents were ordered inside and the Mississippi River and highways were closed, but Westlake later said what was released was mostly steam. A second incident followed in May when part of the plant lost power and vinyl chloride was released, sending three workers to the hospital for inhalation injuries.

It’s the threat of those chemical releases that has gotten the most attention over the decades, with protests and lawsuits focusing on possible health harms, especially among nearby residents.

“This is an example of what it’s like to live along a massive petrochemical corridor,” said Marylee Orr, executive director of the Baton Rouge-based Louisiana Environmental Action Network. “It poses a risk to the workers first and then to the community that lives right along the front line.”

For example, the Williams plant emits substantial amounts of ethylene and propylene, the chemical building blocks that it makes, according to the Environmental Protection Agency’s numbers.

Many who live in the area, though, say they believe they can balance safety and growth.

“We’re always looking for more industry and companies that will employ our residents,” said Turner, the councilman. “We just want that growth to be good growth. We want the companies to follow safe procedures to make sure incidents like this don’t happen.”

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Associated Press writer Michael Kunzelman in New Orleans contributed to this report.